Responsive nanostructures for controlled alteration of interfacial properties

Responsive materials are a class of materials that are capable of “intelligently” changing properties upon exposure to a stimulus. Silk ionomers are introduced as a promising candidate of biopolymers that combine the robust, biocompatible properties of silk fibroin with the responsive properties of poly-l-lysine (PL) and poly-l-glutamic acid (PG). These polypeptides can be assembled using the well-known technique of layer-by-layer processing, allowing for the creation of finely tuned nanoscale multilayers coatings, but their properties remain largely unexplored in the literature. Thus, this research explores the properties of silk ionomer multilayers assembled in different geometries, ranging from planar films to three-dimensional microcapsules with the goal of created responsive systems. These silk ionomers are composed of a silk fibroin backbone with a variable degree of grafting with PG (for anionic species) or PL or PL-block- polyethylene glycol (PEG) (for cationic species). Initially, this research is focused on fundamental properties of the silk ionomer multilayer assemblies, such as stiffness, adhesion, and shearing properties. Elastic modulus of the materials is considered to be one of the most important mechanical parameters, but measurements of stiffness for nanoscale films can be challenging. Thus, we studied the applicability of various contact mechanics models to describe the relationship between force distance curves obtained by atomic force microscopy and the stiffness of various polymeric materials. Beyond considerations of tip size, we also examine the critical regions at which various commonly used indenter geometries are valid. Following this, we employed standard AFM probes and colloidal probes coated with covalently bonded silk ionomers to examine the friction and adhesion between silk ionomers layers. This technique allowed us to compare the interactions between silk ionomers of different chemical composition by using multilayer films containing standard silk ionomers or silk ionomers grafted with polyethylene glycol PEG. This led to the unexpected result that the PEG grafted silk ionomers experienced a higher degree of adhesion and a larger friction coefficient compared to the standard silk ionomers. Next, we move to microscale responsive systems based on silk ionomer multilayers. The first of these studies looks at the effect of assembly pH and chemical composition on the ultimate properties of hollow, spherical microcapsules. This study shows that all compositions and processing conditions yield microcapsules that show a substantial change in elastic modulus, swelling, and permeability, with maximum changes in property values (from acidic pH to basic pH) of around a factor of 6, 1.5, and 5, respectively. In addition, it was discovered that the use of acidic pH assembly inverts the permeability response (i.e. causes a drastic reduction in permeability at higher pH), whilst the use of PEG largely damps any observable trend in permeability, without adversely affecting the swelling or elastic modulus responses. In the second part of these studies, we constructed tri-component photopatterned arrays for the purpose of creating self-rolling films. This study demonstrated that the ultimate geometry of the final rolled shape can be tuned by controlling the thickness of various components, due to the creation of a stress mismatch at high pH conditions. Additionally, it was revealed that pH-driven, semi-reversible delamination of silk ionomers from polystyrene exhibited a change in both magnitude and wavelength with the addition of methanol treated silk fibroin as a top layer. Finally, we showcase examples of biologically compatible systems that incorporate non-polymeric materials in order to generate tunable optical behavior. In one study, we fabricated composite nanocellulose-silk fibroin meshes that contained genetically engineered bacteria that acted as chemically sensitive elements with a fluorescent response. The addition of silk fibroin was found to drastically improve the mechanical properties of the cellulose composite structures, safely contain the bacteria to prevent efflux into the medium, and protect the cells from moderate ultraviolet radiation exposure. The final study concludes with the creation of a self-assembled segmented gold-nickel nanorod array used as a responsive element when anchored into a hydrogen-bonded polymer multilayer. Because of the mild tethering conditions and the magnetic nickel component, the nanorods were able to tilt in response to an external magnetic field. This, in turn, allowed for the creation of a never before reported magnetic-plasmonic system capable of continuously-shifting multiple surface polariton scattering peaks (up to 100 nm shifts) with nearly complete reversibility and rapid (<1 s) response times. Overall, this research develops the understanding of the fundamental properties of several different species of silk ionomers and related polymeric materials. This understanding is then utilized to fabricate pH-responsive systems with drastic changes in modulus, permeability, and geometry. In the end, the research prototypes two types of systems with optical responses and chemical/magnetic stimuli, using materials that are chemically (i.e. silk fibroin-based) or structurally (i.e. multilayers) translatable to future work on silk ionomers. These projects all serve the purpose of advancing the understanding of materials and assembly strategies that will allow for the next generation of bioinspired responsive materials.Ph.D

Surface Chemistry of Halloysite Nanotubes. As investigated by adsorption reactions and imaging analysis

Interest in halloysite clay minerals has increased steadily over the last 20+ years, in part, due to their nanotubular shape and size, high aspect ratio and potential technological applications (Churchman et al., 2016). Throughout this thesis the surface chemistry of halloysite nanotubes is investigated by employing several analytical and advanced microscopy techniques to obtain a greater understanding of their internal and external surface features and surface adsorption reactions. This multifaceted analysis approach investigates a range of tubular halloysites of two morphologies, cylindrical and polygonal prismatic, where comparison of the two forms a framework for the presentation and discussion of the results. The results presented in Chapter 3 demonstrate the phosphate adsorption capacity of halloysite nanotubes is influenced by pH and maximum adsorptions of 1.3 mg/g and 0.5 mg/g were obtained for the cylindrical and polygonal prismatic morphologies respectively. Use of advanced microscopy techniques in Chapter 4 showed the external surface of the polygonal prismatic nanotubes have multiple steps and edges, which may act as additional adsorption sites, as has been shown for other clay minerals (Siretanu et al., 2016). In addition, use of cross-section transmission electron microscopy provided evidence of the link between the two morphologies, where the cylindrical nanotubes appear to be the template from which the larger polygonal prismatic nanotubes grow, as previously postulated by Hillier et al. (2016). In further novel work (Chapter 5), gold nanotags have been functionalised with a variety of anionic and neutral terminated linkers and used as nanoscale probes to study adsorption to the surface of halloysite nanotubes Here, transmission electron microscopy proved that the adsorption occurred primarily on the nanotube inner lumen and edges. The final technical chapter, Chapter 6, focuses on the structure and dynamics of interlayer water in halloysite through the use of neutron scattering techniques, where the initial results demonstrated that the interlayer water appears to move via both rotations and translations within the interlayer. The research presented ascertains that the surfaces of the halloysite nanotubes are more complex than often depicted for technological applications and that the specific tubular morphology is important in the functionality and behaviour of the nanotubes. This fundamental work contributes towards optimisation of halloysite nanotubes for technological applications

Optical properties and self assembly of biotemplated gold nanoparticle chains

Gold nanochains are assembled on amyloid fibers and their optical properties are investigate

An investigation of mechanics in nanomachining of Gallium Arsenide

The first two decades of the 21st Century have seen a wide exploitation of Gallium Arsenide (GaAs) in photoemitter device, microwave devices, hall element, solar cell, wireless communication as well as quantum computation device due to its superior material properties, such as higher temperature resistance, higher electronic mobility and energy gap that outperforms silicon. Ultra-precision multiplex two dimensional (2D) or three dimensional (3D) free-form nanostructures are often required on GaAs-based devices, such as radio frequency power amplifiers and switches used in the 5G smart mobile wireless communication. However, GaAs is extremely difficult to machine as its elastic modulus, Knoop hardness and fracture toughness are lower than other semiconductor materials such as silicon and germanium. This PhD thesis investigated the mechanics of nanomachining of GaAs through molecular dynamics (MD) simulation combined with single point diamond turning (SPDT) and atomic force microscope (AFM) based experimental characterization in order to realise ductile-regime nanomachining of GaAs, which is the most important motivation behind this thesis. The investigation of mechanics of nanomachining of GaAs included studies on cutting temperature, cutting forces, origin ductile plasticity, atomic scale friction, formation mechanism of sub-surface damage, wear mechanism of diamond cutting tool. Machinability of GaAs at elevated temperature was also studied in order to develop thermally-assisted nanomachining process in the future to facilitate plastic material deformation and removal. This thesis contributed to address the knowledge gaps such as what is the incipient plasticity, how does the sub-surface damage form and how does the diamond cutting tool wear during nanomachining of GaAs. Firstly, this thesis investigated the cutting zone temperature, cutting forces and origin of plasticity of GaAs material, including single crystal GaAs and polycrystalline GaAs during SPDT process. The experimental and MD simulation study showed GaAs has a strong anisotropic machinability. The simulation results indicated that the deformation of polycrystalline GaAs is accompanied by dislocation nucleation in the grain boundaries (GBs) leading to the initiation of plastic deformation. Furthermore, the 1/2 is the main type of dislocation responsible for ductile plasticity in polycrystalline GaAs. A phenomenon of fluctuation from wave crests to wave troughs in the cutting forces was only observed during cutting of polycrystalline GaAs, not for single-crystal GaAs. Secondly, this thesis studied the atomic scale friction during AFM-based nanomachining process. a strong size effect was observed when the scratch depths are below 2 nm in MD simulations and 15 nm from the AFM experiments respectively. A strong quantitative corroboration was obtained between the MD simulations and the AFM experiments in the specific scratch energy and more qualitative corroboration with the pile up and the kinetic coefficient of friction. This conclusion suggested that the specific scratch energy is insensitive to the tool geometry and the speed of scratch used in this investigation but the pile up and kinetic coefficient of friction are dependent on the geometry of the tool tip. Thirdly, this thesis investigated formation mechanism of sub-surface damage and wear mechanism of diamond cutting tool during nanomachining of GaAs. Transmission Electron Microscope (TEM) measurement of sub-surface of machined nanogrooves on GaAs and MD simulation of dislocation movement indicated the dual slip mechanisms i.e. shuffle-set slip mechanism and glide-set slip mechanism, and the creation of dislocation loops, multi dislocation nodes, and dislocation junctions governed the formation mechanism of sub-surface damage of GaAs during nanomachining process. Elastic-plastic deformation at the apex of the diamond tip was observed in MD simulations. Meanwhile, a transition of the diamond tip from its initial cubic diamond lattice structure sp3 hybridization to graphite lattice structure sp2 hybridization was revealed. Graphitization was, therefore, found to be the dominant wear mechanism of the diamond tip during nanometric cutting of single crystal GaAs. Finally, in MD simulations study of cutting performance at elevated temperature, hotter conditions resulted in the reduction of cutting forces by 25% however, the kinetic coefficient of friction went up by about 8%. While material removal rate was found to increase with the increase of the substrate temperature, it was accompanied by an increase of the sub-surface damage in the substrate. Moreover, a phenomenon of chip densification was found to occur during hot cutting which referred to the fact that the amorphous cutting chips obtained from cutting at low temperature will have lower density than the chips obtained from cutting at higher temperatures.The first two decades of the 21st Century have seen a wide exploitation of Gallium Arsenide (GaAs) in photoemitter device, microwave devices, hall element, solar cell, wireless communication as well as quantum computation device due to its superior material properties, such as higher temperature resistance, higher electronic mobility and energy gap that outperforms silicon. Ultra-precision multiplex two dimensional (2D) or three dimensional (3D) free-form nanostructures are often required on GaAs-based devices, such as radio frequency power amplifiers and switches used in the 5G smart mobile wireless communication. However, GaAs is extremely difficult to machine as its elastic modulus, Knoop hardness and fracture toughness are lower than other semiconductor materials such as silicon and germanium. This PhD thesis investigated the mechanics of nanomachining of GaAs through molecular dynamics (MD) simulation combined with single point diamond turning (SPDT) and atomic force microscope (AFM) based experimental characterization in order to realise ductile-regime nanomachining of GaAs, which is the most important motivation behind this thesis. The investigation of mechanics of nanomachining of GaAs included studies on cutting temperature, cutting forces, origin ductile plasticity, atomic scale friction, formation mechanism of sub-surface damage, wear mechanism of diamond cutting tool. Machinability of GaAs at elevated temperature was also studied in order to develop thermally-assisted nanomachining process in the future to facilitate plastic material deformation and removal. This thesis contributed to address the knowledge gaps such as what is the incipient plasticity, how does the sub-surface damage form and how does the diamond cutting tool wear during nanomachining of GaAs. Firstly, this thesis investigated the cutting zone temperature, cutting forces and origin of plasticity of GaAs material, including single crystal GaAs and polycrystalline GaAs during SPDT process. The experimental and MD simulation study showed GaAs has a strong anisotropic machinability. The simulation results indicated that the deformation of polycrystalline GaAs is accompanied by dislocation nucleation in the grain boundaries (GBs) leading to the initiation of plastic deformation. Furthermore, the 1/2 is the main type of dislocation responsible for ductile plasticity in polycrystalline GaAs. A phenomenon of fluctuation from wave crests to wave troughs in the cutting forces was only observed during cutting of polycrystalline GaAs, not for single-crystal GaAs. Secondly, this thesis studied the atomic scale friction during AFM-based nanomachining process. a strong size effect was observed when the scratch depths are below 2 nm in MD simulations and 15 nm from the AFM experiments respectively. A strong quantitative corroboration was obtained between the MD simulations and the AFM experiments in the specific scratch energy and more qualitative corroboration with the pile up and the kinetic coefficient of friction. This conclusion suggested that the specific scratch energy is insensitive to the tool geometry and the speed of scratch used in this investigation but the pile up and kinetic coefficient of friction are dependent on the geometry of the tool tip. Thirdly, this thesis investigated formation mechanism of sub-surface damage and wear mechanism of diamond cutting tool during nanomachining of GaAs. Transmission Electron Microscope (TEM) measurement of sub-surface of machined nanogrooves on GaAs and MD simulation of dislocation movement indicated the dual slip mechanisms i.e. shuffle-set slip mechanism and glide-set slip mechanism, and the creation of dislocation loops, multi dislocation nodes, and dislocation junctions governed the formation mechanism of sub-surface damage of GaAs during nanomachining process. Elastic-plastic deformation at the apex of the diamond tip was observed in MD simulations. Meanwhile, a transition of the diamond tip from its initial cubic diamond lattice structure sp3 hybridization to graphite lattice structure sp2 hybridization was revealed. Graphitization was, therefore, found to be the dominant wear mechanism of the diamond tip during nanometric cutting of single crystal GaAs. Finally, in MD simulations study of cutting performance at elevated temperature, hotter conditions resulted in the reduction of cutting forces by 25% however, the kinetic coefficient of friction went up by about 8%. While material removal rate was found to increase with the increase of the substrate temperature, it was accompanied by an increase of the sub-surface damage in the substrate. Moreover, a phenomenon of chip densification was found to occur during hot cutting which referred to the fact that the amorphous cutting chips obtained from cutting at low temperature will have lower density than the chips obtained from cutting at higher temperatures

Metal Nanoparticles/Nanowires Self-assembly on Ripple Patterned Substrate: Mechanism, properties, and applications

Plasmonic properties of self-assembled silver nanoparticles/nanowires array on periodically patterned Si (100) substrate are reported with special attention on the mechanism of nanoparticles self-assembly. The advantage of this bottom up approach over other self-assembling and lithographic methods is the flexibility to tune array periodicity down to 20 nm with interparticle gaps as low as 5 nm along the ripple. Ripple pattern have shallow modulation (~2 nm) still particles self-assembly was observed in non-shadow deposition. Therefore adatoms diffusion and kinetics is important on ripple surface for the self-assembly. PVD e-beam evaporation method used for deposition has proven to be superior to sputter deposition due to lower incident flux and lower atom energy. It was found that particles self-assembly largely dependent on angle of incidence, substrate temperature, and deposition direction due to ripple asymmetric tilt. Ostwald ripening observed during annealing on ripples substrate has striking dependency on ripple periodicity and was found to be different compared to Ostwald ripening on flat Si surface. In-situ RBS measurements of deposited silver on flat and rippled substrate confirmed different sticking of atoms on the two surfaces. The difference between maximum and minimum of the calculated local flux show a peak at an incidence angle of 70o with respect to surface normal. This explains the best alignment of particles at this angle of incidence compare to others. Self-assembled nanoparticles are optically anisotropic, i.e. they exhibit a direction dependent shift in LSPR. The reason of the observed anisotropy is a direction dependent plasmonic coupling. Different in plane and out of the plane dielectric coefficients calculated by modelling Jones matrix elements, confirms that nanoparticle/nanowire array are biaxial anisotropic (ex ¹ ey ¹ ez). The nanoparticles are predominantlyinsulating while nanowires are both metallic and insulating depending on the dimension. Silver nanoparticles/nanowires self-aligned on pre-patterned rippled substrate are presented for the first time as an active SERS substrate. Anisotropic SERS response in such arrays is attributed to different field enhancement along and across the ripples. Strong plasmonic coupling in elongated nanoparticles chain results in significantly higher SERS intensity then spherical nanoparticles/nanowires and non-ordered nanoparticles. Higher SERS intensity across the nanowires array in comparison to along the array (bulk silver) confirms electromagnetic field enhancement (hot-junction) is responsible for SERS phenomenon. Self-assembly of cobalt nanoparticle on ripple pattern substrate is also reported. Due to less adatom mobility and higher sticking cobalt self-assembly is possible only at much higher temperature. A strong uniaxial magnetic anisotropy was observed not observed for non ordered cobalt particles

Metal Nanoparticles/Nanowires Selfassembly on Ripple Patterned Substrate - Mechanism, Properties and Applications

Plasmonic properties of self-assembled silver nanoparticles/nanowires array on periodically patterned Si (100) substrate are reported with special attention on the mechanism of nanoparticles self-assembly. The advantage of this bottom up approach over other self-assembling and lithographic methods is the flexibility to tune array periodicity down to 20 nm with interparticle gaps as low as 5 nm along the ripple. Ripple pattern have shallow modulation (~2 nm) still particles self-assembly was observed in non-shadow deposition. Therefore adatoms diffusion and kinetics is important on ripple surface for the self-assembly. PVD e-beam evaporation method used for deposition has proven to be superior to sputter deposition due to lower incident flux and lower atom energy. It was found that particles self-assembly largely dependent on angle of incidence, substrate temperature, and deposition direction due to ripple asymmetric tilt. Ostwald ripening observed during annealing on ripples substrate has striking dependency on ripple periodicity and was found to be different compared to Ostwald ripening on flat Si surface. In-situ RBS measurements of deposited silver on flat and rippled substrate confirmed different sticking of atoms on the two surfaces. The difference between maximum and minimum of the calculated local flux show a peak at an incidence angle of 70o with respect to surface normal. This explains the best alignment of particles at this angle of incidence compare to others. Self-assembled nanoparticles are optically anisotropic, i.e. they exhibit a direction dependent shift in LSPR. The reason of the observed anisotropy is a direction dependent plasmonic coupling. Different in plane and out of the plane dielectric coefficients calculated by modelling Jones matrix elements, confirms that nanoparticle/nanowire array are biaxial anisotropic (ex ¹ ey ¹ ez). The nanoparticles are predominantly insulating while nanowires are both metallic and insulating depending on the dimension. Silver nanoparticles/nanowires self-aligned on pre-patterned rippled substrate are presented for the first time as an active SERS substrate. Anisotropic SERS response in such arrays is attributed to different field enhancement along and across the ripples. Strong plasmonic coupling in elongated nanoparticles chain results in significantly higher SERS intensity then spherical nanoparticles/nanowires and non-ordered nanoparticles. Higher SERS intensity across the nanowires array in comparison to along the array (bulk silver) confirms electromagnetic field enhancement (hot-junction) is responsible for SERS phenomenon. Self-assembly of cobalt nanoparticle on ripple pattern substrate is also reported. Due to less adatom mobility and higher sticking cobalt self-assembly is possible only at much higher temperature. A strong uniaxial magnetic anisotropy was observed not observed for non ordered cobalt particles

Focusing and delivery of laser radiation for nano- and microfabrication

The recent advances in nanotechnology and nanofabrication motivate the drive to achieve a tighter focusing of light; this requires a high numerical aperture (NA) optical system. The need for high optical resolution has led scientists to discover the use of optical microlens for improving the performance of high numerical aperture (NA) optical systems. By focusing the laser beam through a microlens, the width of the beam can be reduced according to the needs of the application. In this work, the laser beam was focused by a microspherical lens (NA=0.7) into 150 nm or by tapered fibre into 4 μm diameter spots. The measurements indicate the strong influence of tightly focused beams. This thesis comprises of three parts; the first results chapter investigates the choice of material by considering the material properties and feasibility of fabrication (chapter 2). It has been shown in previous studies that the glass transition temperature of the polymer is an important factor in determining the laser ablation rate. High glass transition temperatures make it a good material candidate for optical waveguides. Polycarbonate (PC), polymethylmethacrylate (PMMA), negative photoresist SU-8, and chitosan have been characterised to choose suitable material as a substrate for soft nanolithography (chapter 3). The choice of material due to the glass transition temperature of the material (from literature), material optical properties are investigated experimentally at the range of wavelength from 190 nm to 1000 nm. Laser ablation experiments on PC, PMMA, SU- 8 and chitosan using a 193 nm ArF laser over a fluence range of 10 mJcm−2 –1000 mJcm−2. The ablation threshold at 193nm was found to be 24, 110, 40, and 95 mJ.cm-2 for PC, PMMA, SU-8, and chitosan respectively. The photoresist SU-8 and chitosan were chosen as both materials are biocompatible, and have a high glass transition temperature. Optical properties measured for these materials found that both materials have much higher absorption coefficients (αSU-8 ~ 4.2×105m-1 and αchitosan ~3.3×105m-1) compared with PC and PMMA (αPC =1×105m-1 and αPMMA=2×105m-1 )at 193 nm.The second part of this thesis reports experimental and computational results of an irradiated laser microsphere supported on biocompatible materials; SU-8 photoresist and chitosan (chapter 3). An ArF excimer laser (193 nm wavelength) was used with 11.5 ns pulse width to modify the underlying substrate, producing a single concave dimple. Atomic force microscopy and scanning electron microscope measurements have been used to quantify the shape and size of laser inscribed dimple. The dimple has a diameter of 150 ± 10 nm FWHM and a depth of 190 ± 10nm on SU-8 compared to 180 ± 10 nm FWHM and a depth of 350 ± 10nm on chitosan due to the optical properties of the materials. Finite-difference time-domain (FDTD) simulations were carried out to simulate the propagation of 193 nm laser radiation, focussed by a 1 µm diameter silica sphere. Finite Element Method (FEM) simulations were carried out to calculate laser- induced temperature rise of the both SU-8 and Chitosan layer beneath the microsphere. The SiO2 microsphere acts as a small ball lens tightly focussing the laser radiation. Delivery of the focussed laser radiation locally heats the substrate beneath the microsphere. As a consequence, mass transport takes place, forming a nano dimple.The third part of this thesis presents the use of a CO2 laser (10.6 μm wavelength) for producing microlenses at the end of silica optical fibre (chapter 4). By focused CO2 laser beam, silica optical fiber is irradiated and heated to the softening points (1800 K) of the silica material. Surface tension and the parameters of the fabrication system shape the melted material into a spherical micro-lens or tapered fiber that remains joined to the optical fiber. Different core diameters (125, 400, 600, 1000, and 1500 μm) of multimode fibres have been used for this fabrication. The roughness of the microlens was reduced to less than 20 ± 1 nm roughness by polishing the surface with a CO2 laser at low power (1- 2 W). Throughout this work, different microlenses (ball/parabolic) and tapered fibres were fabricated at the end of silica optical fibre. The minimum spot diameter at FWHM was close to 160 μm and 110 μm for microball and parabolic lenses, respectively. While the tapers had the minimum waist diameters down to 4 μm and maximum taper length of ~ 3.5 mm using silica multi-mode fibre. Finally, the knife-edge technique and He-Ne laser beam (632.8 nm wavelength) were coupled into a fibre to investigate the properties of the microlenses which produced a minimum spot size of 5 ±1 μm at FWHM in the focal region of the tapered fibre lenses of 125, 400 and 600 μm core diameter of the fibre.As a result, Chitosan and SU-8 have been used as substrate materials for recording tightly focussed focal regions, 193nm ArF laser has been used to realise extremely small, 150nm diameter, Photonic Nano Jets (PNJ’s). FDTD optical simulations accurately predict the spatial properties of microsphere PNJ’s emitting at 193. CO2 laser (10.6 μm) radiation has been used to form tapers and spherical lenses on the distal end of optical fibres. Finally, tight focusing using microspheres and lensed optical fibres could be integrated on lab-on- chip platforms for applications such as optical trapping and cell membrane modifications. An important application related to the results of this study is that focusing laser light produces a force that can be used to remove or trap selected cells or large tissue areas from living cell culture down to a resolution of individual single cells and subcellular components similar to organelles or chromosomes, respectively.The nanostructures fabricated in this chapter can be refined to achieve specific dimensions in; diameter, depth, shape, and periodicity so they can be used as antireflective surfaces for solar-cell applications [1].or could be used in drug delivery [2]. While laser microbeams are frequently used for measurement or imaging of biological parameters as well as using the optical tweezer system for trapping or moving of cells, the future medical applications will be focused on micromanipulation or microdissection methods for delivering molecules or nano drugs into a cell [3]. Delivering such nano- drugs into cancer cells requires overcoming the cell membrane by focusing the laser. This phenomenon is named photoporation which is based on the generation of localized transient pores in the cell membrane using the photonic nano jet [4]

Investigation of pulsed laser induced dewetting in nanoscopic metal films

Hydrodynamic pattern formation (PF) and dewetting resulting from pulsed laser induced melting of nanoscopic metal films have been used to create spatially ordered metal nanoparticle arrays with monomodal size distribution on SiO_{\text{2}}/Si substrates. PF was investigated for film thickness h\leq7 nm < laser absorption depth \sim11 nm and different sets of laser parameters, including energy density E and the irradiation time, as measured by the number of pulses n. PF was only observed to occur for E\geq E_{m}, where E_{m} denotes the h-dependent threshold energy required to melt the film. Even at such small length scales, theoretical predictions for E_{m} obtained from a continuum-level lumped parameter heat transfer model for the film temperature, coupled with the 1-D transient heat equation for the substrate phase, were consistent with experimental observations provided that the thickness dependence of the reflectivity of the metal-substrate bilayer was incorporated into the analysis. The spacing between the nanoparticles and the particle diameter were found to increase as h^{2} and h^{5/3} respectively, which is consistent with the predictions of the thin film hydrodynamic (TFH) dewetting theory. These results suggest that fast thermal processing can lead to novel pattern formation, including quenching of a wide range of length scales and morphologies.Comment: 36 pages, 11 figures, 1 tabl

Profiling to Probing: Atomic force microscopy to characterize nano-engineered implants

Surface modification of implants in the nanoscale or implant nano-engineering has been recognized as a strategy for augmenting implant bioactivity and achieving long-term implant success. Characterizing and optimizing implant characteristics is crucial to achieving desirable effects post-implantation. Modified implant enables tailored, guided and accelerated tissue integration; however, our understanding is limited to multicellular (bulk) interactions. Finding the nanoscale forces experienced by a single cell on nano-engineered implants will aid in predicting implants’ bioactivity and engineering the next generation of bioactive implants. Atomic force microscope (AFM) is a unique tool that enables surface characterization and understanding of the interactions between implant surface and biological tissues. The characterization of surface topography using AFM to gauge nano-engineered implants' characteristics (topographical, mechanical, chemical, electrical and magnetic) and bioactivity (adhesion of cells) is presented. A special focus of the review is to discuss the use of single-cell force spectroscopy (SCFS) employing AFM to investigate the minute forces involved with the adhesion of a single cell (resident tissue cell or bacterium) to the surface of nano-engineered implants. Finally, the research gaps and future perspectives relating to AFM-characterized current and emerging nano-engineered implants are discussed towards achieving desirable bioactivity performances. This review highlights the use of advanced AFM-based characterization of nano-engineered implant surfaces via profiling (investigating implant topography) or probing (using a single cell as a probe to study precise adhesive forces with the implant surface)